Feeling Guilty About Not Flossing? Maybe There’s No Need

For decades, the federal government — not to mention your dentist — has insisted that daily flossing is necessary to prevent cavities and gums so diseased that your teeth fall out.

Turns out, all that flossing may be overrated.

The latest dietary guidelines for Americans, issued by the Departments of Agriculture and Health and Human Services, quietly dropped any mention of flossing without notice. This week, The Associated Press reported that officials had never researched the effectiveness of regular flossing, as required, before cajoling Americans to do it.

In a statement issued on Tuesday, the American Academy of Periodontology acknowledged that most of the current evidence fell short because researchers had not been able to include enough participants or “examine gum health over a significant amount of time.”

The revelation has caused a stir among guilt-ridden citizens who strive to floss daily but fall short of that lofty goal. Among experts, however, it has been something of an open secret that flossing has not been shown to prevent cavities or severe periodontal disease.

A review of 12 randomized controlled trials published in The Cochrane Database of Systematic Reviews in 2011 found only “very unreliable” evidence that flossing might reduce plaque after one and three months. Researchers could not find any studies on the effectiveness of flossing combined with brushing for cavity prevention.

“It is very surprising that you have two habits, flossing and toothbrushing without fluoride, which are widely believed to prevent cavities and tooth loss, and yet we don’t have the randomized clinical trials to show they are effective,” said Dr. Philippe Hujoel, a professor of oral health sciences at the University of Washington in Seattle.

The American Dental Association’s website says flossing “is an essential part of taking care of your teeth and gums.” Last year, Dr. Edmond R. Hewlett, a spokesman for the group and a professor of restorative dentistry at the University of California, Los Angeles, said, “We’re confident that disturbing the bacteria in plaque with brushing and flossing is, indeed, beneficial.”

Actually, that is only half proved: Brushing with fluoride does prevent dental decay. That flossing has the same benefit is a hunch that has never been proved.

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If it is any consolation, there is some mediocre evidence that flossing does reduce bloody gums and inflammation known as gingivitis. That Cochrane review found that regular brushers and flossers had less gum bleeding than people who only brushed, although the authors cautioned that the quality of the evidence was “very low.”

Early gingivitis is a long way from severe periodontal disease. Still, some dentists argue that despite a lack of rigorous study, flossing matters if it can reverse initial gum problems.

“Gum inflammation progresses to periodontitis, which is bone loss, so the logic is if we can reduce gingivitis, we’ll reduce the progression to bone loss,” said Dr. Sebastian G. Ciancio, the chairman of the department of periodontology at the University at Buffalo.

Severe periodontal disease may take five to 20 years to develop.

“It’s a very insidious, slow, bone-melting disease,” said Dr. Wayne Aldredge, the president of the American Academy of Periodontology, who practices in Holmdel, N.J.

Even without rigorous evidence that flossing prevents late-stage periodontal disease, Dr. Aldredge urges his patients to floss. Those who quit are “rolling the dice,” he said.

“You don’t know if you’ll develop periodontal disease, and you can find out too late,” he said.

Maybe the evidence that flossing reduces tooth decay or gum disease does not hold up because we are all such poor flossers. Superflossers, like the zealous hygienist at your dentist’s office, aim to “hug the neck of the tooth” and get below the gum line, Dr. Hujoel said.

But we common folk, staring woefully at our bathroom mirrors, tend to lightly give it the once-over.

A review of six trials found that when professionals flossed the teeth of children on school days for almost two years, they saw a 40 percent reduction in the risk of cavities.

So maybe perfect flossing is effective. But scientists would be hard put to find anyone to test that theory.

A version of this article appears in print on August 3, 2016, on Page A10 of the New York edition with the headline: Feeling Guilty About Not Flossing? Maybe There’s No Need. Order Reprints|Today's Paper|Subscribe